Wondering if there's any difference in quality shooting:

1) 1280 60p @ 60fps - then slow down to 30fps in timeline
2) 1280 30p @ 60fps - already appears slow in timeline

anyone know if one method is "better" ? or saves on memory?
I'm guessing they're the same

You loose audio when over/under cranking. But not with 60p.

And I think the bit rate is higher when over cranking vs 60p. Someone can correct me if I remember wrong.

ahhh - thanks!

Olof is right:

overcranking does not record sound.
And it takes twice the memory: it is saved as if it is a 30fps file twice as long as the recorded time.
Imagequality wise overcranking gives you the better image.
Plus you don't need to reinterpret the footage in your NLE.

"Image quality wise overcranking gives you the better image."

Why would this be?

Because you have 35 Mbps. But in overcranking a second is 2 seconds long.

still don't understand - why is overcranked quality better?

When the datarate is higher there is less compression, so the images are cleaner.

Over cranking uses a higher bitrate that is the reason it is cleaner.

Ok to put it more clear. You are recording at 35 Mbps (Mega bits per second) that is the compression of the file. When you overcrank to 50/60 Fps, you will get 70 Mbps. Twice the data rate = Half as much compression = twice the amount of information kept = Better image.

But in the weird bitrate scheme of those XDCAM EX cameras, a (non-overcranked) 35Mbps 720p60 stream is actually already less compressed than a 1080p30 stream that the camera also saves as 35Mbps, which is used as standard... having 70Mbps for the same is pretty much overkill.

I've checked the difference between the 2 ways to do it, and frankly I couldn't notice any difference in quality. Knowing I still have sound, and don't have files that are twice as big to store, I prefer the 720p60 route.
That might depend on the NLE you use too, personally in Premiere it's just a matter of setting "Interpret Footage" to 30fps (or 25 in my case for PAL), and that's it, no rendering time or other drawbacks, it's done on the fly.

Another benefit of shooting overcranked is that you can immediately review the clip on camera in slowmotion. This way it's easier to check whether the shot is any good as slowmo.